In any offshore discovery of a hydrocarbon containing reservoir such as one holding crude oil and/or gas, a considerable time elapses between the actual time of discovery and the date when a flow of usable hydrocarbon is realized. The primary causes of delay are the necessary factors that go into preparing the site and the equipment so that wells can be drilled and the product extracted from the reservoir.
Essentially, the reservoir or the formation and its environment must be tested to determine the condition of the soil, and as near as possible the conditions at the hydrocarbon formation or reservoir. Thereafter, and with this material in hand, a marine structure can be designed to be installed at the offshore site. The usual structure is capable of holding equipment for drilling the necessary wells and handling the resulting flow of product from these wells.
An essential facet of any such structure or platform is the presence of drill conductors which function to guide a drill string as well as to form a conduit for drilling fluids. Said conductors normally comprise a series of tubular members which are incorporated into the offshore structure as it is being constructed. Under some circumstances the conductors can be driven into the formation by the drilling rig or vessel.
Frequently, the marine structure is provided with a series of vertically aligned and spaced apart conductor guides. Thereafter, when a well is to be drilled, a conductor is lowered through the respective guides to assure a generally vertical disposition in anticipation of a drill string being passed therethrough.
The design and building of an appropriate offshore structure is contingent to a large extent on the availability of facilities where the structure will be fabricated. This often requires that a reservation be made months in advance for use of said facilities in order to commence the physical building of the structure.
Thereafter, when the structure has been completed, it is installed by being either floated to its offshore site, or by being barged. When it is properly positioned, it is fixed in place. With the structure's basic jacket located and piled, the remainder of the platform can be completed. The latter includes the positioning of well drilling equipment which is arranged cooperatively with pre-set drill conductors so that the necessary wells can be drilled.
In any event the time schedule for the above noted design, building, installation and ultimate operation of the platform can extend into several years.
During this extended period the reservoir or productive subterranean formation will remain untapped and serve no useful purpose.
The herein disclosed method provides means whereby the offshore hydrocarbon containing formation or reservoir can be tapped or provided with a number of producing wells within a relatively limited time period. While at least some of the wells are thereafter provisionally producing usable product, the support structure can be designed, built and subsequently installed to facilitate further drilling and production.
The disclosed offshore structure is thus adapted to utilize an auxiliary drilling vessel or ship to commence the production process. This however will be a temporary expedient until drilling equipment on the permanent platform can be utilized.
The method herein disclosed resides in the use of a composite marine structure that can be built and installed on a piecemeal basis. This avoids the usual time delay which would otherwise result were the productive field or hydrocarbon containing formation to be provided with a drilling and producing structure in the usual manner.
Physically, a relatively simple drilling template is fabricated which includes a plurality of upright drilling conductors. The function of the latter is to extend downwardly into the ocean floor, and upward for a predetermined distance beyond the water's surface. In such a position they will receive a downwardly moving, rotating drill string such that the latter can penetrate the substrate and concurrently confine a flow of drilling mud.
In any platform utilized for offshore drilling, normally a drilling conductor is inserted into a platform slot only at such times as it is to be used. Thus, and as noted herein, the structure is provided with a series of vertically spaced drilling conductor guides which serve to properly position the conductor as it is lowered from the deck down toward the ocean floor.
As a well is drilled through a prepositioned conductor, the well is subsequently completed, provided with well head equipment, and turned into a producing facility.
In the present arrangement, a provisionally placed drilling vessel is utilized in conjunction with the initially installed drilling template. This is achieved by positioning or anchoring the vessel adjacent to the template. Thereafter, the vessel such as a jack-up rig which is provided with an overhung or outboard drilling platform, can extend over the installed template. The vessel's drilling equipment will thus be in position to penetrate the ocean floor by way of one of the conductors.
Following this procedure, one or more wells can be drilled through a plurality of conductors, at least some of which wells can be producers. These will be connected to the shore or preferably to fluid separating equipment. The latter function to separate the liquid and gaseous products before each is transferred to shore or to a storage facility.
Eventually, the above noted marine structure will be completed at the fabrication yard such that it can be installed in conjunction with the preinstalled drilling template. The platform, following normal design, will include a drilling deck having facilities thereon for continuing the drilling of the wells through the remaining conductors. Thus, the need for the auxiliary drilling vessel will be lessened, even obviated and the further drilling of wells can proceed from the platform itself.
It is therefore an object of the invention to provide a method for facilitating the extraction of hydrocarbon products from an offshore formation in a manner which will permit rapid realization of a usable product without the immediate need for use of an expensive drilling and producing structure.
A further object is to provide means for extracting a hydrocarbon fluid from an offshore reservoir or formation on a provisional basis during the interim period when the permanent marine structure or platform jacket is being fabricated and installed.